There are no tricks to the Seattle rental market. This is a very desirable city with a huge influx of tech employees, whose salaries have pushed most rental prices into the home-mortgage range. Seattle also has generally poor public transit options, so location is critical. Some districts are very protective of their local community, and avoid web sites like Craigslist, instead going with posters in local coffee shops, etc.
Anything furnished, without roommates, with an address in Seattle, is probably going to be in the $1500-3000/mo range. If you are relocating with a company, find out if they have any properties they use for long-term rentals.
Other than that, there are Seattle communities on Reddit where tech community people connect for housing sometimes, too. But really Craigslist is the tool. Best of luck!